1. Field of the Invention
The present invention relates to a method for determining the position of a wafer by means of electron beams and to a wafer having chips for determining the position of the wafer. More particularly, it relates to a method and a chip for determining the position of a wafer in which the chip is given a specific pattern so as to enable accurate determination of the position of the wafer with respect to the electron beams with a small scan width.
2. Description of the Prior Art
Generally, when forming a pattern on a wafer using an electron beam exposure apparatus, the wafer must be positioned to the pattern-forming electron beam with an accuracy of about 0.1 .mu.m.
In one conventional wafer position-determining method, a chip mounted on a wafer and having a large mark is at first scanned in a rough adjusting step using electron beams of secondary electrons, reflected electrons, and so forth, to determine the position of the wafer with an accuracy of about 1 .mu.m. Then, another chip mounted on the wafer and having a small mark is scanned in a fine adjusting step, to determine the position of the wafer with an accuracy of 0.1 .mu.m.
There are problems, however, in the above-mentioned prior art. First, to scan a large mark in the rough adjusting step, a long scan line is required. This, however, leads to destruction of other chips adjacent to the chip having the large mark and to destruction of the mark in one scan as the position-determining beam has the same intensity as the pattern-forming beam.
To resolve these problems, conventionally, a large chip provided with a plurality of large marks has been necessary. This, however, limits the effective use of a wafer.
Second, since the large mark in the rough adjusting chip has a relatively simple shape, it is difficult to distinguish it from dust on the wafer or other patterns on other semiconductor chips.